The present invention relates to an image display apparatus and, more particularly, to a head- or face-mounted image display apparatus that can be retained on the observer's head or face.
A conventional image display apparatus is disclosed in Japanese Patent Application Unexamined Publication (KOKAI) No. 3-101709 (1991). In the conventional image display apparatus, an image that is displayed by an image display device is transmitted as an aerial image by a relay optical system including a positive lens, and the aerial image is projected into an observer's eyeball as an enlarged image by an ocular optical system formed from a concave reflecting mirror.
U.S. Pat. No. 4,669,810 discloses another type of conventional image display apparatus. In this apparatus, an image of a CRT is transmitted through a relay optical system to form an intermediate image, and the image is projected into an observer's eye by a combination of a reflection holographic element and a combiner having a hologram surface.
U.S. Pat. No. 4,026,641 discloses another type of conventional image display apparatus. In this apparatus, an image of an image display device is transferred to a curved object surface by an image transfer device, and the image transferred to the object surface is projected in the air by a toric reflector.
U.S. Reissued Pat. No. 27,356 discloses another type of conventional image display apparatus. The apparatus is an ocular optical system which projects an object surface onto an exit pupil by a combination of a semitransparent concave mirror and a semitransparent plane mirror.
Other known image display apparatuses include those which are disclosed in U.S. Pat. Nos. 4,322,135 and 4,969,724, European Patent No. 0,583,116A2, and Japanese Patent Application Unexamined Publication (KOKAI) No. 7-333551 (1995).
In these conventional techniques, a plurality of optical elements are needed to constitute an ocular optical system, or three or more surfaces are needed to constitute an optical element which forms an ocular optical system. Further, a reflecting surface and a transmitting surface, which constitute an optical system, are formed by using a spherical surface, a rotationally symmetric aspherical surface, a toric surface, an anamorphic surface, etc. Therefore, it has heretofore been impossible to favorably correct ray aberration and distortion at the same time.
If an image for observation is not favorably corrected for both aberration and distortion, the image is distorted as it is viewed by an observer. If the observation image is distorted such that images viewed with the user's left and right eyes are not in symmetry with each other, the two images cannot properly be fused into a single image. In the case of displaying a figure or the like, the displayed figure appears to be distorted, making it impossible to correctly recognize the shape of the displayed figure.